Office chair base



FIG. 1 is a perspective view of an office chair base showing my design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof; and,

FIG. 6 is a top plan view thereof.

The broken line showing in FIG. 2 are for the purpose of illustratingthe environment of the design and form no part of the claimed design.

The ornamental design for an office chair base, as shown and described.